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At least 1,423 records · Page 79Linked to original sources
USGS1995

Water levels in the Calumet aquifer and their relation to surface-water levels in northern Lake County, Indiana, 1985-92

The U.S. Geological Survey made 2,328 water-level measurements at a total of 96 ground-water and surface-water sites in northern Lake County, Indiana, from August 1985 through September 1992. This report lists and summarizes the significance of the measurements. Northern Lake County is on the southern shore of Lake Michigan and includes the cities of East Chicago, Gary, Hammond, and Whiting. The study area is underlain by the unconfined Calumet aquifer and receives about 36 inches of precipitation per year. The U.S. Geological Survey investigated ground-water levels and flow in the Calumet aquifer and the effect of Lake Michigan levels on ground-water and surface-water levels throughout the study area. Summary statistics of the water-level data were computed for each site. Ground-water levels annually reach a maximum in June or July and a minimum in September or October. Measured groundwater fluctuations in the Calumet aquifer during the study period ranged from 0.40 to 5.01 feet, and the mean ground-water fluctuation was about 2.3 feet The largest surface-water fluctuations were affected by record setting Lake Michigan levels. Midmonth daily averages for the data-collection period show that Lake Michigan fluctuated 4.14 feet Water-level fluctuations on the Grand Calumet River were from 1.06 to 2.45 feet. Analysis of water-level data indicates that the 1988 drought did not substantially affect water levels in the Calumet aquifer, but the deficit in precipitation reversed vertical flow gradients in ground water at three paired deep and shallow wells. High water levels in Lake Michigan during 1985-87 created long-term backwater effects on the Grand Calumet River as far as 11.0 miles upstream from Lake Michigan. Analysis of water-level data from the data-collection network indicates that the water table normally slopes toward streams, ditches, sewers, the Indiana Harbor Canal, and Lake Michigan. The slope of the water table toward the Grand Calumet River is greatest in the winter and can decrease to being almost horizontal in the summer. Wells near streams respond quickly to nearby surface-water-level changes. Water-table maps indicate that sewers and dewatering systems are lowering ground-water levels in large areas. Ditches, the Grand Calumet River, and the Indiana Harbor Canal connect the Lake Michigan water level to large parts of the study area. The surface-water stage in the Indiana Harbor Canal, which functions as a ditch, can equal Lake Michigan's stage up to 3.75 miles inland from the lakeshore. Human activity, the stage of Lake Michigan, and the storage capacity of the Calumet aquifer combine to reduce vertical changes in the water table in the study area.

Indiana↗
USGS1992

Techniques for estimating 7-day, 10-year low-flow characteristics for ungaged sites on streams in Mississippi

Mississippi State water laws require that the 7-day, 10-year low-flow characteristic (7Q10) of streams be used as a criterion for issuing wastedischarge permits to dischargers to streams and for limiting withdrawals of water from streams. This report presents techniques for estimating the 7Q10 for ungaged sites on streams in Mississippi based on the availability of baseflow discharge measurements at the site, location of nearby gaged sites on the same stream, and drainage area of the ungaged site. These techniques may be used to estimate the 7Q10 at sites on natural, unregulated or partially regulated, and non-tidal streams. Low-flow characteristics for streams in the Mississippi River alluvial plain were not estimated because the annual lowflow data exhibit decreasing trends with time. Also presented are estimates of the 7Q10 for 493 gaged sites on Mississippi streams. Techniques for estimating the 7Q10 have been developed for ungaged sites with base-flow discharge measurements, for ungaged sites on gaged streams, and for ungaged sites on ungaged streams. For an ungaged site with one or more base-flow discharge measurements, base-flow discharge data at the ungaged site are related to concurrent discharge data at a nearby gaged site. For ungaged sites on gaged streams, several methods of transferring the 7Q10 from a gaged site to an ungaged site were developed; the resulting 7Q10 values are based on drainage area prorations for the sites. For ungaged sites on ungaged streams, the 7Q10 is estimated from a map developed for. this study that shows the unit 7Q10 (7Q10 per square mile of drainage area) for ungaged basins in the State. The mapped values were estimated from the unit 7Q10 determined for nearby gaged basins, adjusted on the basis of the geology and topography of the ungaged basins.

Mississippi↗
USGS2000

Quality-assurance design applied to an assessment of agricultural pesticides in ground water from carbonate bedrock aquifers in the Great Valley of eastern Pennsylvania

Assessments to determine whether agricultural pesticides are present in ground water are performed by the Commonwealth of Pennsylvania under the aquifer monitoring provisions of the State Pesticides and Ground Water Strategy. Pennsylvania's Department of Agriculture conducts the monitoring and collects samples; the Department of Environmental Protection (PaDEP) Laboratory analyzes the samples to measure pesticide concentration. To evaluate the quality of the measurements of pesticide concentration for a groundwater assessment, a quality-assurance design was developed and applied to a selected assessment area in Pennsylvania. This report describes the quality-assurance design, describes how and where the design was applied, describes procedures used to collect and analyze samples and to evaluate the results, and summarizes the quality assurance results along with the assessment results. The design was applied in an agricultural area of the Delaware River Basin in Berks, Lebanon, Lehigh, and Northampton Counties to evaluate the bias and variability in laboratory results for pesticides. The design—with random spatial and temporal components—included four data-quality objectives for bias and variability. The spatial design was primary and represented an area comprising 30 sampling cells. A quality-assurance sampling frequency of 20 percent of cells was selected to ensure a sample number of five or more for analysis. Quality-control samples included blanks, spikes, and replicates of laboratory water and spikes, replicates, and 2-lab splits of groundwater. Two analytical laboratories, the PaDEP Laboratory and a U.S. Geological Survey Laboratory, were part of the design. Bias and variability were evaluated by use of data collected from October 1997 through January 1998 for alachlor, atrazine, cyanazine, metolachlor, simazine, pendimethalin, metribuzin, and chlorpyrifos. Results of analyses of field blanks indicate that collection, processing, transport, and laboratory analysis procedures did not contaminate the samples; there were no false-positive results. Pesticides were detected in water when pesticides were spiked into (added to) samples. There were no false negatives for the eight pesticides in all spiked samples. Negative bias was characteristic of analytical results for the eight pesticides, and bias was generally in excess of 10 percent from the ‘true’ or expected concentration (34 of 39 analyses, or 87 percent of the ground-water results) for pesticide concentrations ranging from 0.31 to 0.51 mg/L (micrograms per liter). The magnitude of the negative bias for the eight pesticides, with the exception of cyanazine, would result in reported concentrations commonly 75-80 percent of the expected concentration in the water sample. The bias for cyanazine was negative and within 10 percent of the expected concentration. A comparison of spiked pesticide-concentration recoveries in laboratory water and ground water indicated no effect of the ground-water matrix, and matrix interference was not a source of the negative bias. Results for the laboratory-water spikes submitted in triplicate showed large variability for recoveries of atrazine, cyanazine, and pendimethalin. The relative standard deviation (RSD) was used as a measure of method variability over the course of the study for laboratory waters at a concentration of 0.4 mg/L. An RSD of about 11 percent (or about ?0.05 mg/L)characterizes the method results for alachlor, chlorpyrifos, metolachlor, metribuzin, and simazine. Atrazine and pendimethalin have RSD values of about 17 and 23 percent, respectively. Cyanazine showed the largest RSD at nearly 51 percent. The pesticides with low variability in laboratory-water spikes also had low variability in ground water. The assessment results showed that atrazinewas the most commonly detected pesticide in ground water in the assessment area. Atrazine was detected in water from 22 of the 28 wells sampled, and recovery results for atrazine were some of the worst (largest negative bias). Concentrations of the eight pesticides in ground water from wells were generally less than 0.3 µg/L. Only six individual measurements of the concentrations in water from six of the wells were at or above 0.3 µg/L, five for atrazine and one for metolachlor. There were eight additional detections of metolachlor and simazine at concentrations less than 0.1 µg/L. No well water contained more than one pesticide at concentra-tions at or above 0.3 µg/L. Evidence exists, how-ever, for a pattern of co-occurrence of metolachlor and simazine at low concentrations with higher concentrations of atrazine. Large variability in replicate samples and negative bias for pesticide recovery from spiked samples indicate the need to use data for pesticide recovery in the interpretation of measured pesti-cide concentrations in ground water. Data from samples spiked with known amounts of pesticides were a critical component of a quality-assurance design for the monitoring component of the Pesti-cides and Ground Water Strategy. Trigger concentrations, the concentrations that require action under the Pesticides and Ground Water Strategy, should be considered maximums for action. This consideration is needed because of the magnitude of negative bias.

Water-Resources Investigations Report↗
USGS1999

Occurrence, distribution, and trends of volatile organic compounds in the Ohio River and its major tributaries, 1987-96

The Ohio River is a source of drinking water for more than 3 million people. Thus, it is important to monitor the water quality of this river to determine if contaminants are present, their concentrations, and if water quality is changing with time. This report presents an analysis of the occurrence, distribution, and trends of 21 volatile organic compounds (VOCs) along the main stem of the Ohio River and its major tributaries from 1987 through 1996. The data were collected by the Ohio River Valley Water Sanitation Commission's Organics Detection System, which monitors daily for VOCs at 15 stations. Various statistical methods were applied to basinwide data from all monitoring stations and to data from individual monitoring stations. For the basinwide data, one or more VOCs were detected in 45 percent of the 44,837 river-water samples. Trichloromethane, detected in 26 percent of the samples, was the most frequently detected VOC followed by benzene (11 percent), methylbenzene (6.4 percent), and the other 18 VOCs, which were detected in less than 4 percent of the samples. In samples from 8 of the 15 monitoring stations, trichloromethane was also the most frequently detected VOC. These stations were generally near large cities along the Ohio River. The median trichloromethane concentration was 0.3 microgram per liter (μg/L), and concentrations ranged from less than 0.1 to 125.3 μg/L. Most of the VOCs had median detected concentrations that ranged from 0.1 to 0.4 μg/L for the basinwide data and for samples from individual stations. Samples from stations in the upstream part of the basin and from the Kanawha River had the highest median concentrations. Ninety-nine percent of the detected VOC concentrations were within U.S. Environmental Protection Agency drinking-water regulations. Of the 268 exceedances of drinking-water regulations, 188 were due to the detection of 1,2-dichloroethane prior to 1993 in samples from the monitoring station near Paducah, Ky. Time trend analyses indicated that most VOCs had no trend in samples at most monitoring stations because they were detected infrequently. At one or more stations, 14 VOCs had decreasing trends in monthly mean concentrations that ranged from -0.01 to -0.42 μ/L per year. Nine VOCs had significant decreasing trends in percentage detection that ranged from -1.08 to -12.90 percent per year. These trends suggest that source-control efforts are working and that water quality is improving.

Ohio River↗
USGS1987

Cost effectiveness of the U.S. Geological Survey's stream-gaging program in Wisconsin

This report presents the results of a three-step evaluation of the stream-gaging program in Wisconsin. First, data uses and funding sources were identified for the 89 continuous-record gaging stations operated during the 1984 water year. Next, alternative methods of streamflow estimation were examined for three stations. A flow-routing model was used for two of the stations and a statistical model was used for the third. The modeled discharges did not compare well enough with observed discharges to warrant elimination of any of the stations. Finally, an optimization model was used to assess the cost effectiveness of the stream-gaging process. The annual budget, in 1984 dollars, for operating the 89 continuous-record gaging stations and 65 additional stations is $557,3000. Based on a Kalman-filter analysis, the theoretical average standard error of instantaneous discharge associated with the current practice of visiting the stations is 13.8%. This overall level of accuracy could be maintained with a budget of $518,6000 if stream-gaging activities were redistributed in an optimal fashion among the gaging stations. For the current budget, the theoretical average standard error would be reduced to 10.1% if the network is operated in an optimal fashion. Furthermore, the average standard error would be reduced to 7.3% if all missing record is eliminated and the network is operated optimally. A minimum budget of $510,000 is required to operate the program; a budget less than this does not permit proper service and maintenance of the gaging stations. At this minimum budget, the theoretical average standard error of instantaneous discharge is 14.4%. The maximum budget analyzed was $650,000 and resulted in an average standard of error of instantaneous discharge of 7.2%.

Wisconsin↗
USGS1998

Base (100-year) flood elevations for selected sites in Marion County, Missouri

The primary requirement for community participation in the National Flood Insurance Program is the adoption and enforcement of floodplain management requirements that minimize the potential for flood damages to new construction and avoid aggravating existing flooding conditions. This report provides base flood elevations (BFE) for a 100-year recurrence flood for use in the management and regulation of 14 flood-hazard areas designated by the Federal Emergency Management Agency as approximate Zone A areas in Marion County, Missouri. The one-dimensional surface-water flow model, HEC-RAS, was used to compute the base (100-year) flood elevations for the 14 Zone A sites. The 14 sites were located at U.S., State, or County road crossings and the base flood elevation was determined at the upstream side of each crossing. The base (100-year) flood elevations for BFE 1, 2, and 3 on the South Fork North River near Monroe City, Missouri, are 627.7, 579.2, and 545.9 feet above sea level. The base (100-year) flood elevations for BFE 4, 5, 6, and 7 on the main stem of the North River near or at Philadelphia and Palmyra, Missouri, are 560.5, 539.7, 504.2, and 494.4 feet above sea level. BFE 8 is located on Big Branch near Philadelphia, a tributary to the North River, and the base (100-year) flood elevation at this site is 530.5 feet above sea level. One site (BFE 9) is located on the South River near Monroe City, Missouri. The base (100-year) flood elevation at this site is 619.1 feet above sea level. Site BFE 10 is located on Bear Creek near Hannibal, Missouri, and the base (100-year) elevation is 565.5 feet above sea level. The four remaining sites (BFE 11, 12, 13, and 14) are located on the South Fabius River near Philadelphia and Palmyra, Missouri. The base (100-year) flood elevations for BFE 11, 12, 13, and 14 are 591.2, 578.4, 538.7, and 506.9 feet above sea level.

Water-Resources Investigations Report↗
USGS2000

Documentation of a computer program to simulate lake-aquifer interaction using the MODFLOW ground water flow model and the MOC3D solute-transport model

Heads and flow patterns in surficial aquifers can be strongly influenced by the presence of stationary surface-water bodies (lakes) that are in direct contact, vertically and laterally, with the aquifer. Conversely, lake stages can be significantly affected by the volume of water that seeps through the lakebed that separates the lake from the aquifer. For these reasons, a set of computer subroutines called the Lake Package (LAK3) was developed to represent lake/aquifer interaction in numerical simulations using the U.S. Geological Survey three-dimensional, finite-difference, modular ground-water flow model MODFLOW and the U.S. Geological Survey three-dimensional method-of-characteristics solute-transport model MOC3D. In the Lake Package described in this report, a lake is represented as a volume of space within the model grid which consists of inactive cells extending downward from the upper surface of the grid. Active model grid cells bordering this space, representing the adjacent aquifer, exchange water with the lake at a rate determined by the relative heads and by conductances that are based on grid cell dimensions, hydraulic conductivities of the aquifer material, and user-specified leakance distributions that represent the resistance to flow through the material of the lakebed. Parts of the lake may become "dry" as upper layers of the model are dewatered, with a concomitant reduction in lake surface area, and may subsequently rewet when aquifer heads rise. An empirical approximation has been encoded to simulate the rewetting of a lake that becomes completely dry. The variations of lake stages are determined by independent water budgets computed for each lake in the model grid. This lake budget process makes the package a simulator of the response of lake stage to hydraulic stresses applied to the aquifer. Implementation of a lake water budget requires input of parameters including those representing the rate of lake atmospheric recharge and evaporation, overland runoff, and the rate of any direct withdrawal from, or augmentation of, the lake volume. The lake/aquifer interaction may be simulated in both transient and steady-state flow conditions, and the user may specify that lake stages be computed explicitly, semi-implicitly, or fully-implicitly in transient simulations. The lakes, and all sources of water entering the lakes, may have solute concentrations associated with them for use in solute-transport simulations using MOC3D. The Stream Package of MODFLOW-2000 and MOC3D represents stream connections to lakes, either as inflows or outflows. Because lakes with irregular bathymetry can exist as separate pools of water at lower stages, that coalesce to become a single body of water at higher stages, logic was added to the Lake Package to allow the representation of this process as a user option. If this option is selected, a system of linked pools (sublakes) is identified in each time step and stages are equalized based on current relative sublake surface areas.

Water-Resources Investigations Report↗
USGS2003

Nitrogen and phosphorus in streams of the Great Miami River Basin, Ohio, 1998–2000

Sources and loads of nitrogen and phosphorus in streams of the Great Miami River Basin were evaluated as part of the National Water-Quality Assessment program. Water samples were collected by the U.S. Geological Survey from October 1998 through September 2000 (water years 1999 and 2000) at five locations in Ohio on a routine schedule and additionally during selected high streamflows. Stillwater River near Union, Great Miami River near Vandalia, and Mad River near Eagle City were selected to represent predominantly agricultural areas upstream from the Dayton metropolitan area. Holes Creek near Kettering is in the Dayton metropolitan area and was selected to represent an urban area in the Great Miami River Basin. Great Miami River at Hamilton is downstream from the Dayton and Hamilton-Middletown metropolitan areas and was selected to represent mixed agricultural and urban land uses of the Great Miami River Basin. Inputs of nitrogen and phosphorus to streams from point and nonpoint sources were estimated for the three agricultural basins and for the Great Miami River Basin as a whole. Nutrient inputs from point sources were computed from the facilities that discharge one-half million gallons or more per day into streams of the Great Miami River Basin. Nonpoint-source inputs estimated in this report are atmospheric deposition and commercial-fertilizer and manure applications. Loads of ammonia, nitrate, total nitrogen, orthophosphate, and total phosphorus from the five sites were computed with the ESTIMATOR program. The computations show nitrate to be the primary component of instream nitrogen loads, and particulate phosphorus to be the primary component of instream phosphorus loads. The Mad River contributed the smallest loads of total nitrogen and total phosphorus to the study area upstream from Dayton, whereas the Upper Great Miami River (upstream from Vandalia) contributed the largest loads of total nitrogen and total phosphorus to the Great Miami River Basin upstream from Dayton. An evaluation of monthly mean loads shows that nutrient loads were highest during winter 1999 and lowest during the drought of summer and autumn 1999. During the 1999 drought, point sources were the primary contributors of nitrogen and phosphorus loads to most of the study area. Nonpoint sources, however, were the primary contributors of nitrogen and phosphorus loads during months of high streamflow. Nonpoint sources were also the primary contributors of nitrogen loads to the Mad River during the 1999 drought, owing to unusually large amounts of ground-water discharge to the stream. The Stillwater River Basin had the highest nutrient yields in the study area during months of high streamflow; however, the Mad River Basin had the highest yields of all nutrients except ammonia during the months of the 1999 drought. The high wet-weather yields in the Stillwater River Basin were caused by agricultural runoff, whereas high yields in the Mad River Basin during drought resulted from the large, sustained contribution of ground water to streamflow throughout the year. In the basins upstream from Dayton, an estimated 19 to 25 percent of the nonpoint source of nitrogen and 4 to 5 percent of the nonpoint source of phosphorus that was deposited or applied to the land was transported into streams.

Ohio↗
USGS1987

Overview of surface-water quality in Ohio's coal regions

This report is designed to provide the nontechnical audience with some of the results of an 'Assessment of Water Quality in Streams Draining Coal-Producing Areas in Ohio,' by Christine L. Pfaff and others (published by the U.S. Geological Survey in 1981). The purpose of the assessment was to document the occurrence of certain chemical constituents in streams in Ohio's coal region and determine to what extent the presence of these constituents was related to mining. Ohio's most productive coal seams are associated with the Allegheny and Monongahela Formation of Pennsylvanian age. These coals were mined by underground methods very early in Ohio's history. Underground mining continues in the state today; however, surface mining now produces significantly more coal. Acid mine drainage from unreclaimed surface and underground mines has affected surface-water quality in Ohio for many years, and recently has led to establishment of reclamation programs by State and Federal agencies. In their assessment of Ohio's coal region, Pfaff and others sampled 150 sites in small watersheds underlain by the Allegheny and the Monogahela Formations. Each site represented only one of four land-use types (active-mine, unmined, abandoned-mine, or reclaimed). Statistical analysis of data from the unmined, abandoned-mine, and reclaimed sites showed that there were significant differences in pH, specific conductance, alkalinity, and concentrations of sulfate and aluminum among abandoned-mine and unmined sites. Reclaimed sites had average pH values and aluminum concentrations similar to those unmined sites. Average specific conductance and sulfate concentrations were about the same for reclaimed abandoned-mine sites, but were significantly lower at unmined sites; specific conductance and sulfate concentration, in fact, proved to be reliable indicators of basins that had been disturbed by mining. Alkalinity was significantly different for all three land uses, the highest values being found at reclaimed sites. The relationship revealed by this study may be useful in designing future water-quality sampling programs in Ohio's coal region.

Water-Resources Investigations Report↗
USGS2001

Relation of shallow water quality in the Central Oklahoma Aquifer to geology, soils, and land use

The purpose of this report is to identify, describe, and explain relations between natural and land-use factors and ground-water quality in the Central Oklahoma aquifer NAWQA study unit. Natural factors compared to water quality included the geologic unit in which the sampled wells were completed and the properties of soils in the areas surrounding the wells. Land-use factors included types of land use and population densities surrounding sampled wells. Ground-water quality was characterized by concentrations of inorganic constituents, and by frequencies of detection of volatile organic compounds and pesticides. Water-quality data were from samples collected from wells 91 meters (300 feet) or less in depth as part of Permian and Quaternary geologic unit survey networks and from an urban survey network. Concentrations of many inorganic constituents were significantly related to geology. In addition, concentrations of many inorganic constituents were greater in water from wells from the Oklahoma City urban sampling network than in water from wells from low-density survey networks designed to evaluate ambient water quality in the Central Oklahoma aquifer study unit. However, sampling bias may have been induced by differences in hydrogeologic factors between sampling networks, limiting the ability to determine land-use effects on concentrations of inorganic constituents. Frequencies of detection of pesticide and volatile organic compounds (VOC's) in ground-water samples were related to land use and population density, with these compounds being more frequently detected in densely-populated areas. Geology and soil properties were not significantly correlated to pesticide or VOC occurrence in ground water. Lesser frequencies of detection of pesticides in water from wells in rural areas may be due to low to moderate use of those compounds on agricultural lands in the study unit, with livestock production being the primary agricultural activity. There are many possible sources of pesticides and VOC's in the urban areas of Central Oklahoma. Because only existing water-supply wells were sampled, it is not clear from the data collected whether pesticides and VOC's: (1) occur in low concentrations throughout upper portions of the aquifer in urban areas, or (2) are present in ground water only in the immediate vicinity of the wells due to back-flow of those chemicals into the wells or to inflow around cement seals and through gravel packs surrounding well casings of surface runoff containing those compounds.

Oklahoma↗
USGS1996

Occurrence of the gasoline oxygenate MTBE and BTEX compounds in urban stormwater in the United States, 1991-95

Methyl tert -butyl ether (MTBE) is a gasoline oxygenate. Oxygenates such as MTBE, when added to gasoline, increase the gasoline's oxygen level and decrease vehicular carbon monoxide emissions and ozone levels in the atmosphere. MTBE disperses rapidly in water, was the second most frequently detected volatile organic compound (VOC) in a study of shallow urban ground water, and is less biodegradable than common gasoline compounds, such as benzene, toluene, ethylbenzene, and total xylene (BTEX). Urban Stormwater is a possible source of MTBE found in shallow ground water. The U.S. Geological Survey (USGS) sampled stormwater in 16 cities and metropolitan areas that are required to obtain permits to discharge Stormwater from their municipal storm-sewer system into surface water. Concentrations of 62 VOCs, including MTBE and BTEX compounds, were measured in 592 Stormwater samples collected in these cities and metropolitan areas from 1991 through 1995. Concentration data for MTBE and BTEX compounds in stormwater were compiled and analyzed, and the findings are summarized in this report. This effort was part of an interagency assessment of the scientific basis and effectiveness of the Nation's oxygenated fuel program and was coordinated by the Office of Science and Technology Policy, Executive Office of the President. MTBE was the seventh most frequently detected VOC in urban Stormwater, following toluene, total xylene, chloroform, total trimethylbenzene, tetrachloroethene, and naphthalene. MTBE was detected in 6.9 percent (41 of 592) of Stormwater samples collected. When detected, concentrations of MTBE ranged from 0.2 to 8.7 micrograms per liter (µg/L), with a median of 1.5 µg/L. All detections of MTBE were less than the lower limit of the U.S. Environmental Protection Agency (EPA) draft lifetime health advisory (20 µg/L) for drinking water. Eighty-three percent of all detections of MTBE in Stormwater were in samples collected during the October through March season of each year (1991-95), which corresponds with the expected seasonal use of oxygenated gasoline in areas where carbon monoxide exceeds established air-quality standards. The median concentration of MTBE and benzene for all samples was statistically different and higher in samples collected during the October through March season than samples collected during the April through September season. Sixty-six percent of all MTBE detections occurred with BTEX compounds, and a proportionate increase in concentrations was found when these compounds occurred together. The proportionate increase could indicate a common source of MTBE and BTEX for those samples. Toluene and total xylene were the most frequently detected BTEX compounds and the most frequently detected VOCs in these investigations. Detected concentrations of toluene and total xylene ranged from 0.2 to 6.6 µg/L and 0.2 to 15 µg/L with median concentrations of 0.3 and 0.4 iig/L, respectively

Water-Resources Investigations Report↗
USGS2000

Organochlorine pesticides and PCBs in stream sediment and aquatic biota—initial results from the National Water-Quality Assessment Program, 1992–1995

One of the goals of the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey is to assess the status and trends in the nation's water quality and to understand the natural and anthropogenic factors that affect water-quality conditions. This report summarizes the occurrence and distribution of 33 organochlorine compounds in fluvial bed sediment and aquatic biota (whole freshwater fish and freshwater bivalves) sampled by NAWQA investigations between 1991 and 1994. These include historically used insecticides (DDT and metabolites, chlordane and its various components, and dieldrin), some currently used pesticides (permethrin and dacthal) and some industrial chemicals and byproducts (PCBs and hexaclorobenzene). Samples were collected at approximately 500 sites in 19 large hydrologic basins throughout the United States. Contaminant levels in bed sediment and aquatic biota are summarized, first on a national basis, and then by land-use classification (for example, urban, cropland, pasture and rangeland, and forest). Nationally, detection frequencies are highest in sediment and biota for the more persistent organochlorine compounds: total DDT, total chlordane, dieldrin, and total PCBs. Organochlorine compounds were detected more frequently in whole fish than in bivalves or bed sediment. Organochlorine pesticide concentrations were relatively high in agricultural regions with histories of high use. The highest organochlorine compound concentrations in both sediment and biota generally were associated with urban areas. Some organochlorine concentrations in sediment exceeded guidelines for the protection of aquatic organisms. A screening-level comparison of measured organochlorine concentrations in whole fish was made with human health guidelines that are applicable to edible fish. This comparison indicates stream sites at which additional sampling of game fish fillets may be warranted, depending on local patterns of fish consumption. A comparison of current national contaminant levels with previous studies of this scope suggests a gradual decrease in organochlorine contaminant levels, at least in fish.

Water-Resources Investigations Report↗
USGS1979

Low-flow characteristics of Wisconsin streams at sewage-treatment plants and industrial plants

Low-flow characteristics of Wisconsin streams at 397 sewage-treatment plants and 143 industrial plants in 30 river basins are presented in this report. The low-flow characteristics are the annual minimum 7-day mean flow below which the flow will fall on the average of once in 2 years (Q 7,2 ) and the annual minimum 7-day mean flow below which the flow will fall on the average of once in 10 years (Q 7, 10 ). The low-flow characteristics at most sewage-treatment and industrial plants (project stations) were determined by correlating base-flow measurements at the project stations with the concurrent daily mean flow at continuous-record gaging stations in the area. The Q 7, 2 and Q 7,10 discharges determined by a frequency analysis at the continuous-record gaging stations were used to estimate the Q 7,2 and Q 7,10 at the project stations. For some project stations the low-flow characteristics also were determined by frequency analysis at nearby continuous-record gaging stations or correlation analysis at nearby low-flow partial-record stations. The Q 7, 2 values ranged from 0 to 3,770 ft 3 /s and Q 7, 10 values ranged from 2,790 ft 3 /s. The accuracy of the estimated low-flow characteristics is evaluated according to the type and amount of data used to determine the low-flow characteristics. The accuracy determined by the standard error of estimate for the 10-year low flow (SE 7, 10 )) ranged from an average of 18 percent at continuous-record gaging stations to an average of h6 percent when only three base-flow measurements were available.

Wisconsin↗
USGS2002

A three-dimensional numerical model of predevelopment conditions in the Death Valley regional ground-water flow system, Nevada and California

In the early 1990's, two numerical models of the Death Valley regional ground-water flow system were developed by the U.S. Department of Energy. In general, the two models were based on the same basic hydrogeologic data set. In 1998, the U.S. Department of Energy requested that the U.S. Geological Survey develop and maintain a ground-water flow model of the Death Valley region in support of U.S. Department of Energy programs at the Nevada Test Site. The purpose of developing this 'second-generation' regional model was to enhance the knowledge an understanding of the ground-water flow system as new information and tools are developed. The U.S. Geological Survey also was encouraged by the U.S. Department of Energy to cooperate to the fullest extent with other Federal, State, and local entities in the region to take advantage of the benefits of their knowledge and expertise. The short-term objective of the Death Valley regional ground-water flow system project was to develop a steady-state representation of the predevelopment conditions of the ground-water flow system utilizing the two geologic interpretations used to develop the previous numerical models. The long-term objective of this project was to construct and calibrate a transient model that simulates the ground-water conditions of the study area over the historical record that utilizes a newly interpreted hydrogeologic conceptual model. This report describes the result of the predevelopment steady-state model construction and calibration. The Death Valley regional ground-water flow system is situated within the southern Great Basin, a subprovince of the Basin and Range physiographic province, bounded by latitudes 35 degrees north and 38 degrees 15 minutes north and by longitudes 115 and 118 degrees west. Hydrology in the region is a result of both the arid climatic conditions and the complex geology. Ground-water flow generally can be described as dominated by interbasinal flow and may be conceptualized as having two main components: a series of relatively shallow and localized flow paths that are superimposed on deeper regional flow paths. A significant component of the regional ground-water flow is through a thick Paleozoic carbonate rock sequence. Throughout the flow system, ground water flows through zones of high transmissivity that have resulted from regional faulting and fracturing. The conceptual model of the Death Valley regional ground-water flow system used for this study is adapted from the two previous ground-water modeling studies. The three-dimensional digital hydrogeologic framework model developed for the region also contains elements of both of the hydrogeologic framework models used in the previous investigations. As dictated by project scope, very little reinterpretation and refinement were made where these two framework models disagree; therefore, limitations in the hydrogeologic representation of the flow system exist. Despite limitations, the framework model provides the best representation to date of the hydrogeologic units and structures that control regional ground-water flow and serves as an important information source used to construct and calibrate the predevelopment, steady-state flow model. In addition to the hydrogeologic framework, a complex array of mechanisms accounts for flow into, through, and out of the regional ground-water flow system. Natural discharges from the regional ground-water flow system occur by evapotranspiration, springs, and subsurface outflow. In this study, evapotranspiration rates were adapted from a related investigation that developed maps of evapotranspiration areas and computed rates from micrometeorological data collected within the local area over a multiyear period. In some cases, historical spring flow records were used to derive ground-water discharge rates for isolated regional springs. For this investigation, a process-based, numerical model was developed to estimat

Water-Resources Investigations Report↗
USGS1994

Land use in, and water quality of, the Pea Hill Arm of Lake Gaston, Virginia and North Carolina, 1988-90

The City of Virginia Beach currently (1994) supplies water to about 400,000 people in southeastern Virginia. The city plans to withdraw water from the Pea Hill Arm of Lake Gaston to meet projected water needs of the population to the year 2030. The purpose of this report is to (1) describe the temporal and spatial distribution of selected water-quality constituents, (2) document current (1989) land use and land cover in the Pea Hill Arm drainage basin, and (3) discuss relations, if any, between the quality of water in the inlets within the Pea Hill Arm and land uses. The report focuses on water-quality problems in the basin, including changes in concentrations of major ions, nutrients, and algae associated with urban development adjacent to water bodies. The Pea Hill Arm was classified as mesotrophic on the basis of the range of concentrations of total phosphorus (0.001 to 0.61 milligrams per liter); the range of concentrations of total organic-plus-ammonia nitrogen (0.2 to 1.4 milligrams per liter); and the range of concentrations of chlorophyll a (1.4 to 56 micrograms per liter). These water-quality data were collected at 3 feet below the water surface during water years 1989-90. Thermal stratification in Pea Hill Arm generally began in April and ended in September. Water below a depth of about 25 feet generally became anoxic by June. Destratification generally began in late September and was completed by November. Lake Gaston followed the same general stratification and destratification pattern as Pea Hill Arm, except Lake Gaston was partially destratified during the summer when large amounts of water were released from John H. Kerr Reservoir and Lake Gaston Dams. During water year 1988, streamflows were 33 percent below the long-term mean-annual streamflows at one of the major streams to Lake Gaston. Low streamflows contributed to elevated specific conductances and concentrations of sodium, calcium, magnesium, and alkalinity from October 1988 to February 1989 at sampling stations in the Pea Hill Arm and Lake Gaston. About 75 percent of the land use in the Pea Hill Arm is forest land. The remaining 25 percent of the Pea Hill Arm drainage basin is 8 percent pasture/open land, 8 percent open water, 6 percent residential land, and 3 percent cropland. No statistical relations are present between water-quality constituents measured and developed land uses within 11 basins in the Pea Hill Arm Basin, except during periods of stormwater runoff. During a stormwater-runoff event, there was a relation between total nitrite plus nitrate and land use (Kendall's tau correlation coefficient of 0.69). The relation between the developed land use and total nitrite plus nitrate can also be related to the increased ground-water inputs during high base-flow periods. Spatial differences in water-quality constituents as determined by Wilcoxon (matched-pairs) signed-rank tests and cluster analyses were longitudinal and primarily grouped into riverine, transition, and lacustrine zones. These zones were grouped on the basis of flow characteristics and nutrient concentrations.

North Carolina, Virginia↗
USGS2000

Distribution, movement, and fate of nitrate in the surficial aquifer beneath citrus groves, Indian River, Martin, and St. Lucie Counties, Florida

The surficial aquifer system beneath citrus groves in Indian River, Martin, and St. Lucie Counties, Florida, was studied to determine the effects of citrus agriculture on ground-water quality. The surficial aquifer is the primary drinking-water source for Martin and St. Lucie Counties and furnishes about 33 percent of the drinking-water for Indian River County. Water-quality samples and water-level data were collected from December 1996 through October 1998. Nitrate concentrations in ground water exceeded 10 milligrams per liter (mg/L), the U.S. Environmental Protection Agency's maximum contaminant level for nitrate reported as nitrogen, in 5 percent of the samples from citrus groves. These exceedances occurred in samples from wells with depths of 10 feet or less at citrus groves, and mostly in samples collected during or immediately following fertilizer applications. Samples from wells with depths of 20-25 feet contained little or no nitrate. The decreased nitrate concentrations in ground water with depth was not consistent with chloride and dissolved-solids concentrations, two other common indicators of agricultural activity. Chloride and dissolved-solids concentrations remained elevated in ground-water samples from all depths at citrus groves; median chloride and dissolved-solids concentrations in samples from citrus sites were 125 and 779 mg/L, respectively. In comparison, samples from the reference site had maximum chloride and dissolved-solids concentrations of 61 and 366 mg/L, respectively. Based on the age of ground water at 20-25 foot depths (3-50 years, measured with tritium and helium-3 concentration ratios), nitrate concentrations also should have remained elevated with depth because fertilizers have been used for at least 20-30 years at these citrus groves. Nitrate concentrations decreased with depth as a result of denitrification. This could have occurred because favorable conditions for denitrification existed in the aquifer, including high concentrations of dissolved organic carbon and iron (median concentrations of 25.5 and 1.75 mg/L, respectively at citrus sites) and low concentrations of dissolved oxygen (median concentration of 0.9 mg/L at citrus sites), which indicates that reducing conditions were present. Evidence that denitrification occurred included the enrichment of ground water with depth in the heavier isotope of nitrogen, nitrogen-15 ( 15 N). Ground water from wells screened 10-15 feet below land surface had a median d 15 N value of 24.6 per mil, whereas ground water from wells screened 5-10 feet below land surface had a median d 15 N value of 9.4 per mil. Fertilizer samples had a median d 15 N value of 3.0 per mil. Increased d 15 N values coincident with decreased nitrate concentrations with depth indicates that fractionation occurred during denitrification reactions. Finally, excess nitrogen gas, a byproduct of denitrification reactions, was detected at concentrations ranging from 0-8 mg/L in samples from wells screened 10-25 feet below land surface.

Florida↗
USGS1994

Water quality of the Apalachicola-Chattahoochee-Flint and Ocmulgee River Basins related to flooding from Tropical Storm Alberto; pesticides in urban and agricultural watersheds; and nitrate and pesticides in ground water, Georgia, Alabama, and Florida

This report presents preliminary water-quality information from three studies that are part of the National Water-Quality Assessment (NAWQA) Program in the Apalachicola-Chattahoochee-Flint (ACF) River basin and the adjacent Ocmulgee River basin. During the period July 3-7, 1994, heavy rainfall from tropical storm Alberto caused record flooding on the Ocmulgee and Flint Rivers and several of their tributaries. Much of the nitrogen load transported during the flooding was as organic nitrogen generally derived from organic detritus, rather than nitrate derived from other sources, such as fertilizer. More than half the mean annual loads of total phosphorus and organic nitrogen were trans- ported in the Flint and Ocmulgee Rivers during the flood. Fourteen herbicides, five insecticides, and one fungicide were detected in floodwaters of the Ocmulgee, Flint, and Apalachicola Rivers. In a second study, water samples were collected at nearly weekly intervals from March 1993 through April 1994 from one urban and two agricultural watersheds in the ACF River basin, and analyzed for 84 commonly used pesticides. More pesticides were detected and at generally higher concentrations in water from the urban watershed than the agricultural water- sheds, and a greater number of pesticides were persistent throughout much of the year in the urban watershed. Simazine exceeded U.S. Environmental Protection Agency (EPA) drinking-water standards in one of 57 samples from the urban watershed. In a third study, 38 wells were installed in surficial aquifers adjacent to and downgradient of farm fields within agricultural areas in the southern ACF River basin. Even though regional aquifers are generally used for irrigation and domestic- and public-water supplies, degradation of water quality in the surficial aquifers serves as an early warning of potential contamination of regional aquifers. Nitrate concentrations were less than 3 mg/L as N (indicating minimal effect of human activities) in water from about two-thirds of the wells. Water from the remaining wells had elevated nitrate con- centrations, probably the result of human activity. Nitrate concentrations in two of these wells exceeded EPA drinking-water standards. Water samples from eight wells had pesticide concentrations above method detection limits. With the exception of two samples for shallow ground-water wells and one surface-water sample from the urban watershed, concentrations of nitrate nitrogen and detected pesticides were below EPA standards and guidelines for drinking water. However, concentrations of the insecticides chlorpyrifos, carbaryl, and diazinon in the surface-water samples approached or exceeded guidelines for protection of aquatic life.

Alabama, Florida, Georgia↗
USGS1998

Dissolved organic carbon concentrations and compositions, and trihalomethane formation potentials in waters from agricultural peat soils, Sacramento-San Joaquin Delta, California; implications for drinking-water quality

Water exported from the Sacramento-San Joaquin River delta (Delta) is an important drinking-water source for more than 20 million people in California. At times, this water contains elevated concentrations of dissolved organic carbon and bromide, and exceeds the U.S. Environmental Protection Agency's maximum contaminant level for trihalomethanes of 0.100 milligrams per liter if chlorinated for drinking water. About 20 to 50 percent of the trihalomethane precursors to Delta waters originates from drainage water from peat soils on Delta islands. This report elucidates some of the factors and processes controlling and affecting the concentration and quality of dissolved organic carbon released from peat soils and relates the propensity of dissolved organic carbon to form trihalomethanes to its chemical composition. Soil water was sampled from near-surface, oxidized, well-decomposed peat soil (upper soil zone) and deeper, reduced, fibrous peat soil (lower soil zone) from one agricultural field in the west central Delta over 1 year. Concentrations of dissolved organic carbon in the upper soil zone were highly variable, with median concentrations ranging from 46.4 to 83.2 milligrams per liter. Concentrations of dissolved organic carbon in samples from the lower soil zone were much less variable and generally slightly higher than samples from the upper soil zone, with median concentrations ranging from 49.3 to 82.3 milligrams per liter. The dissolved organic carbon from the lower soil zone had significantly higher aromaticity (as measured by specific ultraviolet absorbance) and contained significantly greater amounts of aromatic humic substances (as measured by XAD resin fractionation and carbon-13 nuclear magnetic resonance analysis of XAD isolates) than the dissolved organic carbon from the upper soil zone. These results support the conclusion that more aromatic forms of dissolved organic carbon are produced under anaerobic conditions compared to aerobic conditions. Dissolved organic carbon concentration, trihalomethane formation potential, and ultraviolet absorbance were all highly correlated, showing that trihalomethane precursors increased with increasing dissolved organic carbon and ultraviolet absorbance for whole water samples. Contrary to the generally accepted conceptual model for trihalomethane formation that assumes that aromatic forms of carbon are primary precursors to trihalomethanes, results from this study indicate that dissolved organic carbon aromaticity appears unrelated to trihalomethane formation on a carbon-normalized basis. Thus, dissolved organic carbon aromaticity alone cannot fully explain or predict trihalomethane precursor content, and further investigation of aromatic and nonaromatic forms of carbon will be needed to better identify trihalomethane precursors.

California↗